In many subterranean microbial processes, nutrient selection and injection are controlling factors to successful operations. The microorganisms utilized must be nutritiously sustained and metabolically active and thus able to achieve their specific objective.
Numerous microorganisms suitable for achieving various microbial objectives in subterranean formations are known in the art. In order to achieve a specific microbial objective, suitable microorganisms can be selected and injected into the subterranean formation. Oftentimes, however, endogenous microorganisms well suited for achieving a particular microbial objective are already present within the formation.
Recently, a method was disclosed by Clark, et el. (U.S. Pat. No. 5,083,611 assigned to Phillips Petroleum Company), which overcame many problems associated with microbial nutrient injection methods then known to the art. This newly disclosed method provides for the sequential injection into a subterranean formation of sources of individual nutrient components which are deficient in the subterranean formation so that a complete nutrient medium capable of sustaining substantial microbial activity is formed in the subterranean formation upon injection of the last nutrient source. Each of the nutrient sources is comprised of at least one of the deficient individual nutrient components. Further, each of the nutrient sources, up to and including the next to the last nutrient source injected, is injected in an amount such that at least one individual nutrient component contained therein is retained in the subterranean formation in an amount sufficient for achieving the desired in-situ microbial objective.
The above method prevents the excessive utilization and depletion of nutrient components by microorganisms located in the vicinity of the borehole and also takes advantage of chromatographic retention in order to achieve nutrient media distribution beyond the proximity of the borehole. However, it has been discovered and disclosed by the present application, that in order to achieve biomass production (i.e. microbial growth and/or exopolymer production) to plug high permeability zones within subterranean formations, a specific phosphorus source when used in the method of U.S. Pat. No. 5,083,611 exhibits greater plugging potential than others presently used. The phosphorus source of the present invention is a phosphite which is used in combination with a carbon source, and provides for an unexpected increase in a capacity for biological activity due to the ability of said phosphorus source to be more easily transported as well as its ability to remain stable during exposure to high temperatures. The ability of the nutrients to be transported in-depth is therefore of great importance. Some problems associated with the use of known phosphorus sources such as inorganic phosphates is their tendency to complex with divalent cations within the reservoir which results in poor solubility and heightened difficulty in indepth transport. Also, inorganic polyphosphates hydrolyze at higher temperatures which render them less soluble in hard brines characterized by such temperatures. Thus, the specific use of phosphite salts as the phosphorus source in the above method, significantly contributes to the art of practicing said method.
It is therefore an object of this invention to provide a phosphorus source for use in the state-of-the art nutrient injection for subterranean microbial processes which provides for greatly enhanced transportability and thermal stability of the phosphorus nutrient.
These and other objects of the present invention will become apparent upon inspection of the disclosure and the claims herein provided.